Attenuation correction in nuclear medicine imaging is well known in the art. In particular, it is well known when producing SPECT or PET images to correct the images for the effect of attenuation of the gamma rays used for producing the image by intervening tissue and bone. In particular, it is known to generate an attenuation map (three dimensional image or a series of two dimensional slices) of the region being imaged by the gamma camera and correcting the counts of gamma events based on the attenuation of the tissue and bone between the source of the gamma ray and the detector.
The attenuation image is produced in some prior art devices using a source of gamma rays to produce a nuclear CT (attenuation) image, X-ray based CT attenuation images are used in other prior art devices. Devices which utilize the same detector for acquiring both emission and transmission images have been reported as well as devices which utilize different detectors for acquiring the images. Devices utilizing both single and multiple detectors for acquisition of one or both of the images are also known.
In general, prior art devices which utilize X-rays for producing the attenuation map use separate gantries for the X-ray and gamma ray imaging sub-systems. Systems of this type are described, for example, in U.S. Pat. No. 5,391,877, the disclosure of which is incorporated herein by reference. However, this requires matching between the attenuation maps and the nuclear medicine images. Other systems utilize the same gantry for both the X-ray and gamma ray imaging systems. Such systems are described for example in U.S. Pat. No. 5,376,795, the disclosure of which is incorporated herein by reference.